There are many types of transducers of the active type where the input to the transducer may be altered by other received stimuli at another input to produce an output from the transducer indicative of a change in a particular parameter. For example, a potentiometer or rheostat may be used to electrically indicate a particular physical position relative to an X-Y coordinate system. The shaft encoder is another example of mechanical transducer capable of indicating the position of one element relative to another element. A piezoelectric device can be used to electrically indicate the amount of pressure or weight applied to the device.
One of the primary uses of a transducer is to indicate position. An example of an application for a positional indicating transducer is cursor control devices in text editing apparatus, gaming apparatus and other visual display apparatus. In this particular application, a mechanical control mechanism may be employed to interact with information displayed on the screen of the apparatus. An example of such a control mechanism is U.S. Pat. No. 3,987,685 wherein a transport sphere is coupled with rotatable shafts which represent the position of the device in terms of X and Y coordinates. Other examples of such mechanical control mechanisms are cited in this patent. U.S. Pat. No. 3,728,480 discloses a control mechanism in a gaming apparatus provided with a plurality of rotatable knobs that act as rheostats in providing coordinate information for a cursor on the CRT display.
These control mechanisms employ moving parts which are susceptible to mechanical wear, inaccuracies due to transitional misalignments of component parts or inaccuracies due to mechanical limitations during transitional movement in a direction transverse to generally designated cartesian coordinates. The employment of an electronic position indicating device would at least reduce, if not eliminate, the impact of these disadvantages.
An example of electronic position indicating device is the special pen and tablet wherein the pen makes contact with a general tablet from which certain information is derived indicating the coordinate positions of the pen. While such devices are particularly useful in detailed graphical input display devices, they are much more cumbersome in a text display system where the pen must be held at all times during editing text displayed on the device as well as necessitating the pick up and laying down of the pen each time an editing operation is to be performed. From this particular standpoint, a positional transducer functioning as a cursor position device by simple hand movement such as the type disclosed in U.S. Pat. No. 3,987,685, would be more desirable in text editing systems than a special pen. This is particularly true where such a device would be of the electronic type having no moving parts or components. The simplest form of such a desirable cursor position device would be one responsive to the location of an operator's finger on a special electronic tablet or the like.
U.S. Pat. No. 4,103,252 discloses an electronic cursor positioning tablet having no moving parts where the physical contact of the operator's finger moving across the surface of the device provides coordinate information for movement of a cursor over a visual display in a text editing system. This device functions on the principal of variable capacitance caused by finger movement on the surface of the device in proximity to a plurality of capacitor plates. This device does not employ moving mechanical parts but requires sophisticated electronic circuitry for sensing the variance of capacitance to provide signal outputs representative of X-Y position coordinates.